Screw conveyor operation



Nov. s, 1955 H. NICOLAI ET AL 2,723,021

SCREW CONVEYOR OPERATION United States Patent SCREW CONVEYOR OPERA'I 10NHarold Nicolai, Chicago, and Herbert F. Kolze, Forest Park, Ill.,assignors to Vastine Engineering Company, Inc., Forest Park, Ill., acorporation of Illinois Application .luly 17, 1952, Serial No. 299,398

13 Claims. (Cl. 198-213) Our invention relates to improved screwconveyor operation, and more particularly, to an improved method of andapparatus for screw or worm conveyor operation employing sawdust-likecompactible pulverulent material.

In recent times, the disposal of sawdust or the like particulatecompactible waste materials has become a difficult and complicatedproblem in many industries. One of the methods of disposing of suchmaterials involves picking the particulate materials up in acombustion-supporting gas stream, such as air, and conducting such airborne materials to a suitable furnace for burning the same. As will beappreciated, the particulate materials must be conveyed by suitablemeans and methods to a suction pick-up chamber for this purpose. Also,the conveyor means and method most preferably does not interfere withthe over-all control of the air stream passing through the pick-upchamber. Our invention is particularly concerned with a screw conveyoroperation whereby sawdust is conveyed from a suitable sawdust bin or thelike source to the pick up chamber, without the necessity of introducingair into the pick-up chamber through the sawdust thus conveyed thereto.

We accomplish such screw conveyor operation by choke feeding of sawdustin the screw conveyor of our invention, using a restricted zone or tubethrough which the sawdust is conveyed by the rotating screw or worm, andwherein the sawdust is compacted so as to be rendered substantiallyair-impermeable. Generally, screw conveyors are operated under so-callednormal flow conditions whereby the particulate material being moved bythe conveyor fills the conveyor trough to approximately the level of thescrew shaft, and an open-topped trough may be employed in suchinstances. In choke feeding, however, as carried out in the'instantinvention, the trough is provided at least at the discharge end portionthereof with a closed top so as to define a tubular or cylindrical endportion, and the sawdust isfed therethrough so as to completely ll suchtubular or cylindrical portion.

Although the screw conveyor operation of our invention is uniquelyadapted for use in conveying sawdust for the purposes just described,our invention is also applicable to screw conveyor operation involvingthe use of other materials. Preferably, such materials are resilient orcompactable in'nature and are substantially finely divided pulverulentmaterial. For example, United States Patent No. 2,311,773, issued toRussell M. Patterson, on February 23, 1943, describes a screw conveyoroperation for use with particulate compactible insulating material suchas fibrous material of the character of mineral wool and the like, andour invention is adapted for use with materials of this particularcharacter also.

One of the biggest difficulties arising in the handling of bulkmaterials such as the aforementioned insulating materials, andparticularly waste materials such as sawdust, is the problem presentedby the presence of particles if irregular size in such particulatematerial, and

ice

particularly particles of foreign materials, such as nails, stones andthe like materials which are almost invariably present at least to alimited extent. Although the presence of such irregularities in thematerial afford certain complications, in the operation of open-toppedscrew conveyors (and the instant invention provides an improvement inthis respect), it will be readily appreciated that the presence of theseirregularities during choke feeding operation of a screw conveyor willinvariably cause very great difficulty, and will usually cause damage tothe conveyor itself and/or shearing of the suitable shear pins mountedin the conveyor shaft. In fact, we have found that on repeatedoccasions, during the choke feeding of sawdust in a normal screwconveyor adapted for that purpose, the shearing pins failed repeatedly,as soon as the presence of any extra large chips of wood, stones ornails appeared in the sawdust material being conveyed. Such failurestook place to such an extent that in many instances screw conveyorscould not be suitably used for these purposes.

Our invention consists in a unique improvement in screw conveyoroperation, which overcomes such diiculties. In essence, our inventionconsists in the positioning and rotating of the screw or worm in certainpositional relationships with respect to the conveyor trough and tubulardischarge, and the construction of a conveyor shaft so that it will havea desired amount of liexibility to permit limited radial movement of thescrew during operation.

It is, therefore, an important object of our invention to provide animproved screw conveyor operation, and more particularly, an improvedmethod of and apparatus for screw conveyor operation involving the useof compactable particulate material such as sawdust or the like.

It is a further object of our invention to provide an improved screwconveyor comprising a generally cylindrical tube, a shaft rotatablymounted in said tube, and a continuous helical iin co-rotatably mountedon said shaft in said tube for cooperation therewith to push materialthrough said tube, said tube being radially spaced from the iinperiphery less distance on one side than on the other of the fin.

It is another object of our invention to provide an improved screwconveyor comprising a generally cylindrical tube, a shaft rotatablymounted in said tube, and a continuous helical iin co-rotatably mountedon said shaft in said tube for cooperation therewith to push materialthrough said tube, the shaft longitudinal axis being radially spacedfrom the tube longitudinal axis a short distance to effect normallyolf-center rotation of the ns within the tube, and said shaft beingyieldable to permit full radial movement of the fins within the tubeduring operation of theconveyor.

It is yet a further object of our invention to provide an improved screwconveyor for conveying compactable particulate material, comprising agenerally hemi-cylindrical trough, a shaft rotatably mounted in saidtrough, and a continuous helical fin co-rotatably mounted on said shaftin said trough and radially spaced from said trough an average distancer of 5-10% of the fin diameter, said n being spaced a distance r/ 3-3r/7 from the trough at its down-coming side.

It-is yet another object of our invention to provide an improved methodof conducting sawdust-like compactable pulverulent material from asuitable source to a suction pickup zone, that comprises forcing astream of the material through a restricted zone into the pick-up zoneby rotating a worm in the stream in such restricted zone to compact thematerial therein to render it substantiallyy air` impermeable, andproviding restricting surfaces for delining such restricted zonesurrounding said worm positioned-one-half as close to the worm on-onesideas on the opposite side.

Still a further object of our invention is to provide an improved methodofforcing sawdust-like compactable pulverulent material through asubstantially horizontal tube filled with'such material, that' comprisespositioning onV the tube a substantially co-axial shaft mounting acontinuous helical fin spaced from the tube walls an average distance r,and rotating the shaft so as to' normally but yieldably urge the fin toa distance of 31"/ 7-r/ 3'from the tube in the first down-comingquadrant of the fin rotation.

Other and further objects, features and advantages' ofV ourinvention'will become apparent to those skilled in the art from thefollowing detailed description takenin con'- nectionwith theaccompanying drawings, which illustrate a preferred embodiment thereof.

On the drawings:

Figure l is a side elevational view of an improved screw conveyorembodying our invention;

Figure 2 is a sectional elevational View taken substantially along linell-Ii of Figure l; and

Figure 3 is a top plan View of the discharge end of the screw conveyorof Figure l.

As shown on the drawings:

'in Figure 1, the reference numeral llldesignates generally a screwconveyor embodying the instant invention. The screw conveyor 1Gcomprises a generally hemi-cylindrical trough 11 having an open toppedinlet endf12 and a closed cylindrical or tubular discharge end portion13. The trough 11 is suitably mounted on upright braces near the inletend 12, at 14, near the middle at 415 and near the discharge end 13, at16. Each of the braces 14, 15 and 16 is suitably rigidly mounted uponthe floor F by means of angle irons 17, and the trough 11 is thussupported in substantially horizontal alignment.

The trough 11 is positioned so that' the middle portion thereof and theinlet end 12 are within a sawdust' bin or the like storage room for asource of compactable particulate material, the storage room wall 18being shown partially in Figure l. The discharge portion 13 of thetrough 11 extends through aperture in the bin wall. 18 and merges withan enlarged pick-up chamber indicated generally by the reference numeral19. The pick-up chamber 19 comprises a laterally extending top flangedair-inlet conduit 20, which leads downwardly into a substantiallycubical pick-up chamber proper 21, defined by the top inlet conduit 2;@and a partial top wall 22, an end wall 23, a floor 24 andverticallyextending side walls 25, 25. The'floor 24 is suitably apertured adjacentthe end wall 23 to provide for an outlet into the discharge conduit Z6;which extends the full width of the lioor24, providing for downwardmovement of air from the inlet conduit Zlland sawdust from the screwconveyor discharge 13 to flow downwardly through' the aperture in thefloor 24, into the discharge conduit 26 and laterally outwardlytherefrom, as shown by the arrow at the outlet flange 27 at the lateraldischarge of the discharge conduit 26. lf desired, a by-pass line orother conduit (not shown) may be afhxed to the flange 2S at the oppositeend cf the discharge conduit 26 so as to permit air or sawdust bearingair to flow in the direction indicated by the arrow atthe flange 2Sthrough the discharge conduit 26 and out into a suitable conduit (notshown) affixed to the flange 27 at the lateral discharge of the conduit26. It will thus be appreciated that the air entering the pick-upchamber 21 is controlled by controlling the amount of air entering thetop inlet conduit and the amount of air entering the baci-L side of thedischarge conduit 26 at the flange 28. ln order to obtain the necessarycontrol of the total amount of air and sawdust passing out ofthedischarge chamber 26 at the flange 27,it is necessary to preventuncontrolled amounts of air from passing through the cylindricaldischarge portion of the trough 11, at 13.

A generally rectangular duct dened by a rear exten- `sion ofthe-floor24, rearextensions of the side walls v25,l 25 and a top wall 29 extendssurroundingly of the discharge portion 13 from the pick-up chamber 21back through the apertured bin wall 18 and into the bin. A flange 3f)terminates the rear extension of the top wall 29 and the top portionsof' the upstanding side walls 25, 25 so as to provide suitable fasteningmeans for aliixing the discharge end of the device to the bin wall'18.From the flange 30 rearwardly to the rear end wall 31, the trough 11is-a substantially hemi-cylindrical, open-topped conveyor trough. Fromthe flange 36 forwardly,. the conveyor trough 11 is in the form of thesubstantially cylindrical or tubular discharge portion 13, which extendsforwardly a short. distance. so that the top of the tube 13 terminatesflush with the rear edge of the air inlet conduit 2li, and the bottomportion 13a (from substantially the level of the longitudinal axis ofthe tube 13 to the floor 24) is tapered forwardly in the form of' atruncated right circular cylinder. Preferably, a suitably apertured backwall, as. at 32, coplanar with the-flange 30, extends from the floor 24,the side walls 2S, 25'

and the top 29 to surround the tube 13, but outside the peripherythereof, so as to effectively prevent the passage of air outside thetube 13 but within the rectangular housing duct therefor.

Aligned self-aligning seal-tight bearing assemblies 33 and 34 aresuitably mounted respectively on the rear trough wall 31 and the frontend wall 23 of the pick-up chamber 21, andthe bearing assemblies 33 and34 rotatably mount a shaft 35 extending the full distance therebetween.The shaft 35 comprises a hollow central portion 36, extendingsubstantially the distance between the walls 31y and 23', andV solidshaft nubs 37 and 38 mounted suitably in the bearing assemblies 33 and34 respectively andextending therethrough and into the hollowvcentral'shaft member 36 at each end thereof. The shaft member 36 and theshaft nubs 37 and 38 are suitably attached for co-rotation by means ofshear pins 39, 39, which are adapted to give under high torque loads toprevent damage to the conveyor, as will be fully understood by thoseskilled in the art.

A continuous helical finV 40 is co-rotatably axed to the centralv shaftmember 36, as by welding, and extends from its inlet end 40a, a shortdistance from the rear trough wall 31, to its discharge end40b, whichextends through the tube 13 and forwardly a short distance therefrom, soas to terminate substantially below the middle of the inlet air conduit20. The axial length of the fin 40, which is the distance from the point40a to the point 40h, in this specific embodiment of the invention isapproximately inches, and the fin diameter d istapproximately lO-lZinches. The length of the shaft member 36, whichis substantially thedistance from the end wall.3l to the front wall 23, is-approximately -95inches, and the shaftmember 36 consists of extra heavy two inch I. D.steel pipe having a 27s inch O. D. The hollow shaft mmeber 36 is thussufficiently flexible or yieldable to permita reasonable amount ofradial movement of the lin 40 duringoperation of the conveyor. Thedegree of flexibility in the shaft member 36, at least to the extent ofmaximum flexibility, is essentially a matter of selection for thoseskilled in the art, depending upon the particular use involved, but theminimum degree of flexibility is that sufficient to permit radialmovement of the fin 4l) the fullwidth. of the trough 11, which is thedimension w (Figure 2), as'well asthe full height h (Figure 2) of thetubular discharge portion 13; In general, the shaft member 36issuiiiciently flexible if the centralportion of the continuous fin40may come to rest upon the bottom-ofthe troughll' when the conveyortrough 11 is empty, althoughv other criteria may be used toV ascertainthe desired extentv of .flexibility As: will be explainedin detailhereinafter, the yieldabilityv ofy the member 36V should besuch thattheclogging. forces inthel material generated by the attempted passageof lumps, enlarged particles, and foreign materials such as stones andnails, should be such that the member 36 tends to permit suicient radialmovement of the fin 40 to free such clogged materials, without damagingthe fin 40, or the trough portions 11 and 13, and prior to thegeneration of such high torque forces that the shear pins 39 will give,as will also be explained. The trough 1l and discharge 13 are sopositioned with respect to the tin rit) that the radial movement thereofmay be used to serve the useful purpose of freeing or uncloggingmaterial in the conveyor.

One of the first features of the unique trough and fin arrangement hereinvolved, is that of inclining the bottom of the trough portions 11, 12and 13 slightly downwardly in the direction of How of material in thetrough. As will be appreciated, the instant embodiment calls for thepositioning of the shaft 35 in substantially horizontal alignment andfor the use of a iin 40 of substantially constant diameter d the fullaxial length thereof. lt will be seen that the inlet side 12 of thetrough 11 is spaced downwardly from the n bottom (or the bottom of theperipheral extremities of the fins) a very short distance c, which isabout 5% d, or in this embodiment 1/2 inch. The bottom of the dischargetube 13 is spaced a slightly larger distance b from the bottom of the fm40 at the discharge end 4Gb. The distance b being about f/s to 1?/16inch in the instant embodiment, which is 8.5-9.5% d. It will thus beseen that the bottom of the trough 11 is inclined downwardly at an angleof about 20 minutes below the horizontal, and we have found that thisvery slight downward incline produces a very unusual effect inpreventing the clogging of irregularities in the material being movedforward by the rotation of the fin 40.

Referring now to Figure 2, it will be seen that the shaft longitudinalaxis, represented by the point C, is radially spaced from the tubelongitudinal axis, repref sented'by the point C, a short distance so asto effect normally off-center rotation of the tins 40 within the tube13. As will be seen, the fin 40 is spaced about 1/2 as much distance sfrom the tube 13 on the left hand side (Figure 2) as the distance twhich the n 40 is spaced from the tube 13 on the opposite or right handside. The lateral spacing x of the fin or shaft center C from the tubecenter C in this particular embodiment is Mi inch, and the short sidedistance s is 1/z-inch and the long side distance t is one inch.Proportionately, the distance x is 2.5% d as shown, and it may be withinthe range of about l-9% d, preferably about 2-5% d.

The over-all lateral dimension or width w, as here shown is 111/2`inches, and the average space r from the fin periphery of the tube wallmay be expressed as =7.5% d (d being l0 inches) It will be appreciatedthat the average spacing r must be such that a certain amount of radialmovement of the n 40 will be accommodated, as a result of forcesgenerated by clogging of the material, and the selection of the averagespace r will also depend to a certain extent upon the particle size,compactability of the material, and operating speeds and the like basicconditions. ln general, we have found that, using the fin diameter d asa basic dimension, that the distance r may be about 5-l0% d, andpreferably about 7-9% d. On this basis also, the shorter distance s maybe about and the longer distance t may be about Radially off-setting theshaft laterally or vertically, or preferably both, produces a noticeableimprovement. As here shown, the shaft axis C is radially offset orspaced from the tube axis C a distance y upwardly, which distance y isabout 2% d. Most preferably x or y (or both) is l-3% d. The averagespacing r between the lin periphery and the tube, may be represented asfollows:

h-d alb and is preferably about 31'/ 7; whereas the larger bottomdistance b may be and is preferably about 4r/7. It will be appreciatedthat the distances s and a may be substantially the same, or

as here shown, they may be slightly different, the lateral,

distance s being somewhat smaller. In like manner, the larger distancest and b may be substantially the same, or as here shown, the bottomdistance b may be slightly smaller. On this basis, c is r/ 3.

It will be seen that the short lateral distance s is on the down-comingside of the rotating iin 40, that is, the peripheral edge of the fin 40is moving downwardly when it passes the short side, or short spacing sand is moving upwardly when it passes the long side or long spacing t.The n 40 is thus closest to the tube 13 in the rst downcoming quadrantof the iin rotation.

It will be understood that modifications and variations may be effectedwithout departing from the scope of the novel concepts of the presentinvention.

We claim as our invention:

l. A screw conveyor comprising a generally cylindrical tube, a shaftrotatably mounted in said tube, and a continuous helical iinco-rotatably mounted on said shaft and closely spaced from said tube forcooperation therewith to push material through said tube, said tubebeing radially spaced from the iin periphery less distance on one sidethan on the other of the iin and said tube being radially spaced fromthe iin periphery an average distance of 5-10% of the iin diameteraround the entire periphery of the iin.

2. A screw conveyor comprising a generally cylindrical tube, a shaftrotatably mounted in said tube, and a continuous helical finco-rotatably mounted on said shaft and closely spaced from said tube forcooperation therewith to push material through said tube, said tubebeing radially spaced from the iin periphery less distance on one sidethan on the other of the fm normally during rotation thereof and saidshaft being sufficiently flexible to permit radial movement of said finin said tube in response to clogging forces generated in the material inthe tube `and said tube being radially spaced from the iin periphery anaverage distance of 5-l0% of the fm diameter around the entire peripheryof the fin.

3. A screw conveyor comprising a generally cylindrical tube, a shaftrotatably mounted in said tube, and a continuous helical finco-rotatably mounted on said shaft and closely spaced from said tube forcooperation therewith to push material through said tube, the shaftlongitudinal axis being radially spaced from the tube longitudinal axisa short distance laterally to effect normally olf-center rotation of thelins within the tube and said tube being radially spaced from the finperiphery an average distance of 5-l0% of the lin diameter around theentire periphery of the n.

4. A screw conveyor comprising a generally cylindrical tube, a shaftrotatably mounted in said tube, and a continuous helical iinco-rotatably mounted on said shaft and closely spaced from said tube forcooperation therewith to push material through said tube, the shaftlongitudinal axis being radially spaced from the tube longitudinal axisatshort distance verticallyandlaterally to effect normally off-center`rotation. of. the` ns within` the. tube and said tube being radiallyspaced from the lin periphery an average distance of -l0% of the iindiameter around the entire periphery of the lin, andsaid shaft beingyieldable to permit full radial movement of the tins within the tubeduring operation of the conveyor,

5. A screw conveyor comprising a generally cylindrical tube, a-shaftrotatably mounted in said tube, and a continuous helical linco`rotatably mounted on said shaft and closely spaced from-said tube forcooperation therewith to push material throughsaid tube, said tube beingradially spaced from the fin periphery one-half as much dista'nce ononeA side as on'theopposite side' of thein and said tube being radiallyspaced from the'fin` periphery an average distance of 5-l0% of the'ndiameter around the entireperiphery of the fin.

6l A screw conveyor comprising a generally cylindrical tube,.a` shaftrotatably mounted in said tube, and a continuous helical n co-rotatablymounted on said shaft and closely spaced'from said tube for cooperationtherewith to push material through said tube, said shaft beingsubstantially horizontally aligned and said tube being laterallyoff-center with respect to the shaft longitudinal axis and'saidtubebeing radially spaced from the tin periphery an average distance of5-10% of the fin diameter around the entire periphery of the n.

7. A screw conveyor comprising a generally cylindrical tube; a shaftrotatably mounted in said tube, and a continuous helicalin co-rotatablymounted on said shaft and closely spaced from said tube for cooperationtherewith to push material through said tube and said tube beingradially spaced from the fin periphery an average distance of 5-l0% ofthe iin diameter around the entire periphery of the iin, said shaftbeing substantially horizontally aligned and said'tube being laterallyoff-center with respect to the shaft longitudinal axis and the bottom ofsaid tube being inclined slightly downwardly in the direction of'the Howof the material therein.

8. A screw conveyor comprising a generally cylindrical tube, a shaftrotatably mounted in said tube, and a continuous helical finco-rotatably mounted on said shaft and closely spaced from said tube forcooperation therewith topush materialthrough said tube, the shaftlongitudinal axis being laterally spaced from the tube longitudinal axis1-3`% of the lin diameter and said tube beingradially spaced from thelin periphery an average. distance of 540% of the n diameter around theentire periphery of the fin.

9. A screw conveyor comprising a generally cylindrical tube, a shaftrotatably mounted in said tube, and a continuous helical n co-rotatablymounted on said`shaft and closely spaced from said tube for cooperationtherewith 8 to'push'material through said tube, the shaft longitudinalaxis being spaced upwardly from the tube longitudinal axisv 2% of theiin diameter and being spaced laterally from the tube longitudinal axis2.5% of the iin diameter and said tube being radially spaced from theiin periphery an average distance of 5-l0% of the iin diameter aroundthe entire periphery of the lin.

l0. A screw conveyor for conveying compactible particulate material,comprising a generally cylindrical tube, a shaft rotatably mounted insaid tube, and a continuous helical iin co-rotatably mounted on saidshaft in said tube and radially spaced from said tube an averagedistance rk of 5-l0% of the tin diameter, said tin being spaced adistance r/ 3-3r/7 from the tube at its downcoming side.

l1. A screw conveyor for conveying compactible particulate material,comprising a generally cylindrical tube;

a shaft rotatably mounted in said tube, and a continuous.

helical n co-rotatably mounted on said shaft in said tube and radiallyspaced from said tube an average distance r of 540% of the iin diameter,said fin being spaced a distance 4r/ 7-2r/ 3 from the tube at its bottomand its upcoming side.

l2. A screw conveyor for conveying compactible particulate material,comprising a generally cylindrical tube, a shaft rotatably mounted insaid tube, and a continuous helical tin co-rotatably mounted on saidshaft in said tube and radially spaced from said tube an averagedistance i' of 5-10% of the iin diameter, said lin being spaced adistance r/3-3r/7 from the tube at its top and. at its downcoming side.

13. AV screw conveyor for conveying compactible particulate material,comprising a generally cylindrical tube, a sha -t rotatably mounted insaid tube, and a continuous helical lin co-rotatably mounted on saidshaft in said tube and radially spaced from said tube an averagedistance r of 5-l0% of the fin diameter, said tin being spaced adistance r/ 3 from the tube at its downcoming side, and a distance 41'/7 from the tube at its bottom.

References Cited in the le of this patent UNITED STATES PATENTS1,845,873 Hancock Feb. 16,- 1932 1,866,005 Beaty July 5, 1932 2,332,688Baily Oct. 26, 1943 2,438,637 Jansen Mar. 30, 1948 2,532,318 Mackey Dec.5, 1950 2,614,892 Cherewick Oct. 2l, 1952` 2,616,765 Hill Nov. 4,v 1952FOREIGN PATENTS 371,394 Germany Mar. 15, 1923 523,765 Germany Feb. 2,1930r

